The present invention is directed to a de-rotation system that stabilizes a shaft fairing mounted between an upper hub fairing and a lower hub fairing.
Typically, the aerodynamic drag associated with a rotor hub on a rotary wing aircraft is a significant portion of the overall aircraft drag, typically 25% to 30% for conventional single-rotor helicopters. The rotor system drag increases for a rotary wing aircraft having a counter-rotating, coaxial rotor system primarily due to the dual rotor hubs and the interconnecting shaft therebetween. For high-speed rotary wing aircraft, the increased drag resulting from the counter-rotating, coaxial rotor system may result in a relatively significant power penalty.
The aerodynamic drag of the dual counter-rotating, coaxial rotor system is generated by three main components—the upper rotor hub assembly, the lower rotor hub assembly, and the interconnecting main rotor shaft assembly. The drag contribution may be approximately 40% for each of the hubs, and 20% for the interconnecting main rotor shaft assembly. Typically, a rotor hub fairing arrangement is mounted to each of the upper rotor hub and the lower rotor hub such that overall drag on the rotorcraft is reduced. The interconnecting main rotor shaft between the upper rotor hub assembly and the lower rotor hub assembly, however, is typically exposed.
For a variety of reasons including, but not limited to, reduced drag and low observability, shaft fairings have been developed to cover the exposed interconnecting main rotor shaft. The shaft fairing is mounted to the counter-rotating, coaxial rotor system within a rotational environment between the upper hub fairing and the lower hub fairing through a bearing arrangement.
During some flight conditions, the shaft fairing may undesirably rotate relative the airframe which may increase drag and reduce the low-observability benefits of the shaft fairing.